1. Field of the Invention
The present invention relates to a position controller for an optical element, which can be moved to correct image shake and also radially moved onto and radially removed from an optical axis of an optical system.
2. Description of the Related Art
There has been an increasing number of optical devices such as cameras which are equipped with an anti-shake mechanism (image shake correcting mechanism/ image stabilizing mechanism) that moves a specific optical element such as a lens element or an image sensor (image pickup device) in a plane orthogonal to an optical axis of an optical system to reduce (correct) image shake. In Japanese Unexamined Patent Publication No. 2007-163961, a technique for removing (radially retracting) an image-stabilizing optical element to a position outside an anti-shake driving range (to a position off an optical axis of the optical system) when an optical device that incorporates the anti-shake mechanism moves from an operating state to a lens barrel accommodated state (fully retracted state/non-operating state) in which no pictures are taken has been proposed for the purpose of making a lens barrel compact in size.
The lens barrel disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 2007-163961 is provided, inside a movable ring (provided with at least one lens group) that is capable of moving in an optical axis direction, with a fixed frame, and an oscillating frame is supported by the fixed frame to be movable in a plane orthogonal to the optical axis with steel balls (rollers) held between the oscillating frame and the fixed frame. An image-stabilizing lens group holding frame which holds an image-stabilizing lens group is pivoted on the oscillating frame to be rotatable about a shaft parallel to the optical axis. When an image-stabilizing operation is performed, the oscillating frame is smoothly moved relative to the fixed frame by an actuator via a support using the steel balls. When the lens barrel is accommodated (fully retracted), the moving ring is moved toward the image plane (rearward in the optical axis direction) to approach a CCD mount. Thereupon, a contact portion of the image-stabilizing lens group holding frame comes in contact with a cam surface of a driving portion provided on the CCD mount. A further (rearward) retracting movement of the moving ring causes the contact portion of the image-stabilizing lens group holding frame to slide on the cam surface to thereby rotate the image-stabilizing lens group holding frame about the aforementioned rotational shaft. This rotation of the image-stabilizing lens group holding frame causes the image-stabilizing lens group to be removed (radially moved) from a position on the optical axis. According to such a structure, during the lens barrel retracting operation by which the lens barrel is fully retracted, a load in the optical axis direction is applied to the image-stabilizing lens group holding frame with the cam surface and the contact portion in contact with each other, and this load is also transmitted to the oscillating frame. Since steel balls are held between the oscillating frame and the fixed frame as described above, there is a possibility of dents being formed on the steel ball holding surfaces of the oscillating frame and the fixed frame upon an excessive load (e.g., a severe impact) being applied to the lens barrel in the optical axis direction. Such dents deteriorate the operational accuracy of the oscillating frame. In the above-mentioned Japanese Unexamined Patent Publication No. 2007-163961, as a countermeasure against such a problem, the oscillating frame is positioned on the object side (front side in the optical axis direction) of the fixed frame and is biased in a direction to apply pressure to the steel balls (in a direction to approach the fixed frame) by a biasing spring. Application of a load onto the image-stabilizing lens group holding frame in the optical axis direction by the cam surface of the CCD mount causes the oscillating frame to move toward the object side against the biasing force of the biasing spring, which prevents an excessive load from being applied onto the steel balls.
However, in this structure taught in Japanese Unexamined Patent Publication No. 2007-163961, there is a possibility of the steel balls falling out as a result of the steel ball holding state not being maintained if the degree of freedom in movement of the oscillating frame toward the object side with respect to the fixed frame is excessively high, and accordingly, the biasing spring is required to be capable of providing a biasing force of more than a predetermined magnitude. On the other hand, if the biasing force of the biasing spring is excessively great, the moving load of the oscillating frame on the fixed frame becomes excessively great. Therefore, in order to satisfy a self-contradictory demand for suppressing resistance to movement of the oscillating frame during the image-stabilizing operation while securing the holding of the steel balls, even under the condition in which a pressing force produced via the cam surface of the CCD mount is transmitted to the oscillating frame to thereby cause the oscillating frame to move away from the fixed frame, it becomes extremely difficult to adjust the spring force of the biasing spring.
Additionally, in this structure taught in the above-mentioned Japanese Unexamined Patent Publication No. 2007-163961, loads imposed on the image-stabilizing lens group holding frame in the optical axis direction are unavoidable since the image-stabilizing lens group holding frame is pressed by the cam surface of the CCD mount. The image-stabilizing lens group holding frame is a member for holding a lens group, and the positional accuracy of the image-stabilizing lens group holding frame directly affects the optical performance, so that it is desirable not to impose loads on the image-stabilizing lens group holding frame as much as possible. In addition, since the image-stabilizing lens group holding frame is held by the oscillating frame thereon, the relative position between the contact portion of the image-stabilizing lens group holding frame and the cam surface of the CCD mount varies depending on the position of movement of the oscillating frame, so that it is difficult to precisely determine the mutual contacting point. On this account, a smooth retracting operation of the image-stabilizing lens group holding frame might be sacrificed.